We have established direct and specific effects of LHRH on nuclear estradiol receptor (ERn) in the anterior pituitaries (AP) of female rats. ERn is known to increase dramatically during proestrus (PR), coincident with a steep rise in AP responsiveness to the action of LHRH for LH release, the mechanism of which may be related to the increasing ERn levels under the influence of rising LHRH and estradiol (E2) levels during PR. To test this hypothesis it is proposed to: 1) examine the role of in situ LHRH on the known increases in ERn during PR. Endogenous LHRH release will be blocked by phenobarbital at various time points during PR, E2 maintained at control levels, and the effect of 1/2-4 h LHRH block examined on ERn and LH levels; 2) determine interrelationship, if any, between ERn and corresponding LH levels within AP in response to LHRH. Changes in ERn levels as a dose and temporal response to LHRH and related peptide hormones will be monitored in vivo and in vitro (tissue and dispersed cell perifusion model) in relation to corresponding LH levels; 3) evaluation of the effects of LHRH in other target glands of E2 in comparison to its effects on AP, to determine if tissue-specific or non-specific mechanisms are involved. It is hoped that the above investigations will highlight the physiological significance of the effects of LHRH on ERn in AP. The molecular events, which precede the increase in ERn activity within AP, on exposure to LHRH, remains an intriguing question. The fourth objective, therefore, is to explore the various molecular mechanisms that could be mediating the effects of LHRH on ERn, including i) possible retention/stabilization of ERn by LHRH, ii) decreased/increased proteolytic activity, iii) activation/deactivation of ERn by way of possible phosphorylation/dephosphorylation, iv) evaluation of the presence of LHRH receptors on the nuclear membranes and possible involvement of secondary messengers (Ca++, cAMP, cGMP), and v) delineation of the sub-population of ERn being specifically affected by LHRH. The proposed studies should help in furthering our understanding of the mechanism of LHRH action in AP and provide further insight into the relationship between the actions of LHRH and E2 within the broader goal of synergizing the events of estrous cycle by way of various feedback loops, which may importantly include dynamic changes in the levels of ERn.